1. Field of the Invention
The present invention relates to a supporting member for an electron gun of a cathode ray tube and a method for its production.
2. Discussion of Background
The supporting member for an electron gun is used for insulating and fixing a metal electrode constituting an electron gun of a cathode ray tube. The surface of the supporting member is heated and melted by e.g. a gas burner, and the leg portion of a metal electrode is embedded into the supporting member to a predetermined depth and then fixed by cooling. This process step is called a beading step. The heating temperature of the surface of the supporting member required for this beading step is usually from 1200 to 1500.degree. C. Here, in order to embed the leg portion of the electron gun into the supporting member to a desired depth in a predetermined time, complex adjustment of the air/fuel ratio in the gas or the gas flow rate, is required.
Different electron guns are used by different manufacturers of cathode ray tubes or for different types of cathode ray tubes. Such electron guns have different electrode layouts or different electrode structures. Accordingly, it is desired that supporting members for electron guns can be molded and produced in various shapes easily and with high precision. Further, in order to prevent overheating of the entire supporting member and to heat only the surface layer at a high temperature while maintaining the dimensional precision of the supporting member during the beading step, it is necessary to introduce fine foam into the supporting member.
The supporting member is usually prepared in such a manner that glass as the starting material is not directly press-molded but it is once pulverized into a fine powder, and the glass powder thus obtained is mixed with a binder for molding and then pressed in a mold, followed by baking and sintering.
A solvent may sometimes be used to mix the fine glass powder and the binder efficiently and uniformly. In such a case, the fine glass powder is used in the form of a slurry. The solvent may, for example, be water or an alcohol, or an organic polar solvent such as a ketone may also be used.
In the beading step, an electrode metal is penetrated to a predetermined depth into the supporting member in a predetermined time. Accordingly, it is desired that the surface of the supporting member is rapidly heated to reduce the viscosity of the surface of the supporting member. To meet such a requirement, the heating power of the burner for heating may finely be adjusted to meet the beading time prescribed by a throughput for assembling the electron gun. However, there has been a drawback such that a local deformation of the supporting member is likely to form due to excess heating by the burner, or the job change for every different type is extremely cumbersome.
On the other hand, it is conceivable that while the heating condition by the burner is fixed, supporting members having different compositions may be prepared for the respective different types. However, such is not practical, since the physical properties such as the heat expansion coefficients will be different from one type to another.